I2P is beta software since 2003.[5] Developers emphasize that there are likely to be bugs in the software and that there has been insufficient peer review to date.[6] However, they believe the code is now reasonably stable and well-developed, and more exposure can help development of I2P.

The network itself is strictly message-based (like IP), but there is a library available to allow reliable streaming communication on top of it (similar to TCP, although from version 0.6 there is a new UDP-based SSU transport). All communication is end-to-end encrypted (in total there are four layers of encryption used when sending a message), and even the end points ("destinations") are cryptographic identifiers (essentially a pair of public keys), so that neither sender nor recipient of a message need to reveal their IP address to the other side or to third-party observers.

Many developers of I2P are known only under pseudonyms. While the previous main developer, jrandom, is currently on hiatus, others, such as zzz, killyourtv, and Complication have continued to lead development efforts, and are assisted by numerous contributors.[1]

I2PTunnel is an application embedded into I2P that allows arbitrary TCP/IP applications to communicate over I2P by setting up "tunnels" which can be accessed by connecting to pre-determined ports on localhost.

SAM (Simple Anonymous Messaging) is a protocol which allows a client application written in any programming language to communicate over I2P, by using a socket-based interface to the I2P router.[23]

BOB (Basic Open Bridge) is a less complex app to router protocol similar to "SAM"[24][25]

Several programs provide BitTorrent functionality for use within the I2P network. Users cannot connect to non-I2P torrents or peers from within I2P, nor can they connect to I2P torrents or peers from outside I2P.[27]I2PSnark, included in the I2P install package, is a port of the BitTorrent client named Snark.[28]Vuze, formerly known as Azureus, is a BitTorrent client that includes a plugin for I2P, allowing anonymous swarming through this network.[29] This plugin is still in an early stage of development, however it is already fairly stable. I2P-BT is a BitTorrent client for I2P that allows anonymous swarming for file sharing. This client is a modified version of the original BitTorrent 3.4.2 program which runs on MS Windows and most dialects of Unix in a GUI and command-line environment. It was developed by the individual known as 'duck' on I2P in cooperation with 'smeghead'. It is no longer being actively developed; however, there is a small effort to upgrade the I2P-BT client up to par with the BitTorrent 4.0 release. I2PRufus is an I2P port of the Rufus BitTorrent client.[30]Robert (P2P Software) is the most actively maintained I2PRufus fork. And there is I2P-Transmission.

iMule (invisible Mule) is a port of eMule for I2P network. iMule has not been developed since 2013. iMule is made for anonymous file sharing. In contrast to other eDonkey clients, iMule only uses the Kademlia for proceeding to connect through I2P network, so no servers are needed.

I2Phex is a port of the popular Gnutella client Phex to I2P. It is stable and fairly functional.

A port of Tahoe-LAFS has been ported to i2p. This allows for files to be anonymously stored in Tahoe-LAFS grids.

Currently, Vuze is the only torrent client that makes clearnet (connections not through I2P) torrents available on I2P and vice versa. It has a plugin that connects to the I2P network. If the user adds a torrent initially made for I2P, it will be seeded on both I2P and the clearnet. If a user adds a torrent from the clearnet, it will be seeded on both the clearnet and I2P. For this reason, torrents previously published only on I2P are made available to the entire Internet, and users of I2P can download any torrent on the Internet while maintaining the anonymity of I2P.[31][32]

I2P-Bote is a free, fully decentralized and distributed anonymous email system with a strong focus on security.[33] It supports multiple identities and does not expose email metadata. As of 2015[update], it is still considered beta software. I2P-Bote is accessible via the I2P web console interface or using standard email protocols (i.e. IMAP/SMTP). All bote-mails are transparently end-to-end encrypted and signed by the sender's private key, thus removing the need for PGP or other email encryption software. I2P-Bote offers additional anonymity by allowing for the use of mail relays with variable length delays. Since it is decentralized, there is no centralized email server that could correlate different email identities as communicating with each other (i.e. profiling). Even the nodes relaying the mails do not know the sender, and apart from sender and receiver, only the end of the high-latency mail route and the storing nodes will know to whom (which I2P-Bote address – the user's IP address is still hidden by I2P) the mail is destined. The original sender could have gone offline long before the email becomes available to the recipient. No account registration is necessary, all you have to do in order to use it is create a new identity. I2P-Bote can be installed as an I2P plugin .[34]

I2P also has a free pseudonymous e-mail service run by an individual called Postman. Susimail is a web-based email client intended primarily for use with Postman's mail servers, and is designed with security and anonymity in mind. Susimail was created to address privacy concerns in using these servers directly using traditional email clients, such as leaking the user's hostname while communicating with the SMTP server. It is currently included in the default I2P distribution, and can be accessed through the I2P router console web interface. Mail.i2p can contact both i2p email users, via user@mail.i2p and public internet email users from a user@i2pmail.org address.

I2P-Messenger is a simple Qt-based, serverless, end-to-end-encrypted instant messenger for I2P.[35] No servers can log the user's conversations. No ISP can log with whom the user chats, when, or for how long. As it is serverless, it can make use of I2P's end-to-end encryption, preventing any node between two parties from having access to the plain text. I2P-Messenger can be used for fully anonymous instant communication with persons the user doesn't even know, or, alternatively, to communicate securely and untraceably with friends, family members, or colleagues. In addition to messaging, file transfer is also supported.

I2P-Talk is another simple instant messenger incompatible with I2P-Messenger, but having the same security properties

The Privacy Solutions project,[37] a new organization that develops and maintains I2P software, launched several new development efforts designed to enhance the privacy, security, and anonymity for users, based on I2P protocols and technology.

Release builds of an I2P Router application for Android can be found on the Google Play store under The Privacy Solutions Project's Google Play account or on an F-Droid repository hosted by the developers.[41]

Nightweb is an Android application that utilizes I2P and Bittorrent to share blog posts, photos, and other similar content.[42] It can also be run as a desktop application. It is no longer in development.[43]

Eepsites are Websites that are hosted anonymously within the I2P network. Eepsite names end in .i2p, such as ugha.i2p or forum.i2p. EepProxy can locate these sites through the cryptographic identifier keys stored in the hosts.txt file found within the I2P program directory. Typically, I2P is required to access these eepsites.[47]

.i2p

'I2p' is a pseudo-top-level domain which is only valid within the I2P overlay network scope. .i2pnames are resolved by browsers by submitting requests to EepProxy which will resolve names to an I2P peer key and will handle data transfers over the I2P network while remaining transparent to the browser.[48]

EepProxy

The EepProxy program handles all communication between the browser and any eepsite. It functions as a proxy server that can be used by any web browser.

Peers, I2P nodes

Other machines using I2P that are connected to user's machine within the network. Each machine within the network shares the routing and forwarding of encrypted packets.

Tunnels

Every ten minutes, a connection is established between the user's machine and another peer. Data to and from the user, along with the data for other peers (routed through the user's machine), pass through these tunnels and are forwarded to their final destination (may include more jumps).[49]

netDb

The distributed database that holds information on I2P nodes and I2P eepsites. This database is split up among routers known as "floodfill routers". When a user wants to know how to contact an eepsite, or where more peers are, they query the database.[50]

From August 15, 2015 to August 16, 2015 the first I2P convention was held in Toronto, Ontario.[51] The conference was hosted by a local hackerspace, Hacklab. The conference featured presentations from I2P developers security researchers.

August 15, 2015 mainly had presentations on the past growth of the i2p network, a talk on what happens when companies sell your personal information, and a round-table discussion on general privacy and security topics. The day ended with a CryptoParty which helped to introduce new users to installing I2P, sending secure emails with I2P-Bote, and using I2P along with Vuze.

August 16, 2015 had more technical discussions than the previous day. The talks focused what how to dissuade bad-actors from using the network, how I2P has worked computer connection limits, how to do application development using I2P, and on the development of the Android version. This day ended with a development meeting.